Tough call. I'd guess heroic is about 40% "harder" than normal numbers wise.
You'll have a lot of people telling you that the first boss is just glorified trash on heroic but the truth is if you can't target switch and prioritize well as a group you'll get stomped. The second boss is also probably the hardest up to Gorefiend.
I'd give heroic a try to be honest and see how it goes for you.
My guild have only cleared 8/13 NM, and we just 1 shot the first 3 bosses on HC, so yeah I'd at least try the first 3 before worrying too much about Archimonde.